diff --git a/src/Bundle/ChillPersonBundle/migrations/Version20210326113045.php b/src/Bundle/ChillPersonBundle/migrations/Version20210326113045.php
index 6db7e1521..5113ccce2 100644
--- a/src/Bundle/ChillPersonBundle/migrations/Version20210326113045.php
+++ b/src/Bundle/ChillPersonBundle/migrations/Version20210326113045.php
@@ -22,6 +22,13 @@ final class Version20210326113045 extends AbstractMigration
         return 'Change model relation between Person and AccompagnyingPeriod, without losing datas when going up';
     }
     
+    /**
+     *  === UP ===>
+     *
+     *  Preup and postup functions backup datas and transform them
+     *  before injecting them in the new many-to-many join table.
+     *  In these direction, there is no loss.
+     */
     public function preUp(Schema $schema) : void
     {
         // extract datas
@@ -59,18 +66,47 @@ final class Version20210326113045 extends AbstractMigration
     }
     
     
+    /**
+     *  <=== DOWN ===
+     *
+     *  In predown and postdown we backup datas from jointable, and transform them
+     *  before injecting them back in the many-to-one column 'person_id'.
+     *
+     *  The distinct clause makes that for each group of duplicates, it keeps only the first row in the returned result set.
+     *  Then we have only few lost datas. Lost datas: when many persons for one AccompanyingPeriod (keep only first person)
+     */
+    
+    public function preDown(Schema $schema) : void
+    {
+        // extract datas
+        $query = "SELECT DISTINCT ON (accompanyingperiod_id) accompanyingperiod_id AS id, person_id FROM persons_accompanying_periods ORDER BY id, person_id ASC";
+        $data = $this->connection->prepare($query);
+        $data->execute();
+        foreach ($data as $row)
+        {
+            $id = $row['id'];
+            $personId = $row['person_id'];
+            $this->datas[$id] = "$personId";
+        }
+    }
+    
     public function down(Schema $schema) : void
     {
         // drop join table
-        //$this->addSql('DROP TABLE persons_accompanying_periods');
-        
-        // INFO this dangerous query is commented, then if you go down you must manually :
-        // * insert datas in TABLE chill_person_accompanying_period COLUMN person_id ;
-        // * drop join TABLE persons_accompanying_periods when you are sure it works
+        $this->addSql('DROP TABLE persons_accompanying_periods');
         
         // add column
         $this->addSql('ALTER TABLE chill_person_accompanying_period ADD person_id INT DEFAULT NULL');
         $this->addSql('ALTER TABLE chill_person_accompanying_period ADD CONSTRAINT fk_64a4a621217bbb47 FOREIGN KEY (person_id) REFERENCES chill_person_person (id) NOT DEFERRABLE INITIALLY IMMEDIATE');
         $this->addSql('CREATE INDEX idx_64a4a621217bbb47 ON chill_person_accompanying_period (person_id)');
     }
+    
+    public function postDown(Schema $schema) : void
+    {
+        // insert datas in existing table
+        foreach ($this->datas as $id => $personId) {
+            $SQL = "UPDATE chill_person_accompanying_period SET person_id='$personId' WHERE id='$id'";
+            $this->connection->executeQuery($SQL); // CHECK if we have to execute query out of foreach loop. how ?
+        }
+    }
 }